• 대한기계학회논문집A
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• 제28권2호
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• pp.174-180
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• 2004

If Fiber Reinforced Metal Laminates(FRMLs) were delaminated, the decrease of stiffness and fiber bridging effect would result in the sudden aggravation of fatigue characteristics. It was reported that the delamination of FRMLs resulted from the crack of metal layers and that it depended on the crack growth. While cracks were made in FRMLs containing a saw-cuts under fatigue loading, cracks could be produced or not in FRMLs with circular holes under the same condition. When the FRMLs with the circular holes produce not the crack but the delamination, it is not possible to analyze it by the conventional fracture parameters expressed as the function of the crack. And so, this research suggests a new analytical model of the delamination to make the comparison of the delamination behavior possible whenever the cracks occur or not. Therefore, a new analytical model called Pseudo Crack Model(PCM) was suggested to compare the delaminations whether cracks were made or not. The relationship between the crack energy consumption rate( $E_{crack}$) and the delamination energy consumption rate( $E_{del}$) was discussed and it was also known that the effect of $E_{del}$ was larger than that of $E_{crack}$.

• Journal of Biosystems Engineering
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• 제34권5호
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• pp.358-362
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• 2009

This study was conducted to evaluate the performance of a 12 tons capacity circulating concurrent flow rice dryer. An actual scale dryer with the capacity of 12 tons was developed to obtain a faster drying rate of 0.8~1.2%(w.b.)/h, while maintaining a lower drying energy consumption of 5,000 kJ/kg-water and achieving a drying quality that was comparable to a conventional cross-flow rice dryer. The Test-1 was conducted at $110^{\circ}C\;-\;20\;cmm/m^2$ and the Test-2 was conducted at $120-110-100-90^{\circ}C\;-\;20\;cmm/m^2$ under the same conditions as Test-1. In Test-1, the drying rate, drying energy consumption and crack ratio were 0.98 %(w.b.)/h, 4,573 kJ/kg-water and 3.2%, respectively. In Test-2, the drying rate, drying energy consumption and crack ratio were 0.74 %(w.b.)/h, 4,790 kJ/kg-water and 4.0%, respectively. The results of these tests demonstrated that this concurrent-flow dryer reached the desired drying rate, drying energy consumption and crack ratio.

• Journal of Biosystems Engineering
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• 제26권5호
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• pp.469-474
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• 2001

Milling the rice with low moisture requires more energy, produces more cracked rice, and results in reducing taste of cooked rice. Accordingly, it is necessary to add moisture to the rice with low moisture to obtain optimum moisture level for milling and taste of rice. This study was performed to evaluate the influence of initial moisture content and absorption rate on rice crack, milling energy and whiteness of milled rice and to obtain the information for design of rewetting system mounted on stirring device in grain bin. The tests were conducted for the four levels of initial moisture content in the range of 11.4 to 14.5%(w.b.) and six levels of absorption rate in the range of 0.04 to 1.0%, w.b./hr. In the case of lower moisture content below 12%(w.b.), crack ratios of brown rice were remarkably high regardless of initial moisture contents. Therefore, it was found that rough rice below 12%(w.b.) in initial moisture content could not rewetted by spraying water without crack generation of low level. Absorption rate must be below 0.3%, w.b./hr to maintain crack ratio increase of less than 1% regardless of initial moisture contents. In the case of allowable crack ratio increase of 2% and 5%, it was found that the maximum absorprion rate was respectively 0.6%, w.b./hr and 1.0%, w.b./hr in the initial moisture content of above 13.5%(w.b.). Rewetting the rough rice in moisture content of 11.4 to 14.5%(w.b.) to 14.3 to 16.9%(w.b.) decreased milling energy consumption by 15.9 to 22.3%. The effect of energy saving was higher in the samples of higher initial moisture content. Whiteness of milled rice was decreased by 0.5 to 1.5.

• 대한토목학회논문집
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• 제28권4A호
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• pp.529-536
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• 2008

구조물의 파괴 거동은 하중의 재하 속도에 따라 달라지는 특성을 보이는데, 이는 재료의 속도 의존성으로부터 비롯된다고 할 수 있다. 이러한 현상은 공학의 여러 분야에서 관심사였지만, 파괴 메커니즘이 명확히 규명되지 않았기 때문에 수치 해석을 통한 연구에는 그 한계점과 어려움이 상존하였다. 본 연구에서는 파괴 거동의 속도 의존성을 이해하고자, 취성재료를 대상으로 입자동역학을 이용한 수치해석을 수행하였다. 직접 인장 시험 시뮬레이션을 위해 노치가 있는 시편을 모델링하고, 취성재료가 갖는 특성을 표현하기 위해 Lennard-Jones 포텐셜을 사용하였다. 6가지의 다른 하중 속도에 따른 균열의 거칠기, 균열의 후퇴와 멈춤, 분기 현상과 같은 동적 파괴 특성을 관찰하였다. 해석 결과를 통해 하중 속도에 따른 파괴 거동의 변화 원인을 에너지 유입-소모율의 개념을 도입하여 설명하고, 재료의 파괴 메커니즘이 갖는 속도 의존성에 대해 이해할 수 있는 단초를 마련하였다. 또한, 기존 실험과의 비교를 통해 실제적인 현상과의 유사성을 밝힘으로써 입자동역학의 공학적 적용 가능성을 제시하였다.

• Advanced Composite Materials
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• 제16권2호
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• pp.95-113
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• 2007

Experimental investigations of interlaminar mechanical properties for carbon fiber reinforced plastic (CFRP) laminates were carried out using aramid fiber ($Kevlar^{(R)}$-29 1000d) and carbon fiber (TR40-1K 612d, Mitsubishi Rayon) stitching. Various carbon fiber (CF) stitch densities were used to prepare a number of CF stitched CFRP laminates for double cantilever beam (DCB) tests. An insert tongue-type loading fixture, developed by the Japan Aerospace Exploration Agency (formerly the National Aerospace Laboratory of Japan), was also employed in the DCB test. Interlaminar tension tests were carried out under an out-of-plane directional loading using a single CF stitch thread in the CFRP laminates. The DCB test results clarified that the relationship between the volume fractions of the CF stitch thread ($V_{ft}$) and mode I critical energy release rate ($G_{Ic}$) showed a mostly linear function with a higher gradient than that of the $Kevlar^{(R)}$ stitched CFRP laminates. The CF stitched CFRP tension test results indicated that the consumption energy per unit area ($E_i$) was larger than that of $Kevlar^{(R)}$ stitched CFRP laminates.

• Journal of Biosystems Engineering
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• 제22권2호
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• pp.199-209
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• 1997

A one-pass rice whitener with hard metal blades was developed to solve the problems of the existing one-pass rice whitener. The developed one-pass rice whitener was tested and improved through various milling experiments. It showed high performance such as the capacity of 3.5 t/h, the energy consumption of $1.0 kWh/100kg$, milled rice recovery of 91.6%, broken rice rate of 2.2%, the crack rate of 1.9% at the 750 rpm of the roller shaft, compared with those other domestic and foreign one-pass rice whiteners. Especially, it could whiten broun rice of high moisture (16～l7%) with water sprayed at low internal pressure of less than $0.2 kg/cm^2$ and low temperature due to the characteristics of the cutting part composed of 24 hard metal blades. The developed one-pass rice whitener was industrilized and distributed to some rice processing complexs in one fourth price compared with that of imported one-pass rice whiteners.

• 한국표면공학회지
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• 제44권1호
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• pp.7-12
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• 2011

The effect of organic additives, polyethylene glycol (PEG), on the trivalent chromium electroplating was analysed in the view point of current efficiency, solution stability and metallurgical structure. It was measured that PEG-containing trivalent chromium solution had about 10% higher current efficiency than pure solution and controlled the micro-crack density of electrodeposits. PEG exhibited profound effect on the solution stability by reducing the consumption rate of formic acid which acts as a complexant to lower the activation energy required for electrochemical reduction of trivalent chromium ions. It was also revealed that the formation of chromium carbide layer was facilitated in the presence of polyethylene glycol, which meant easier electrochemical codeposition of chromium and carbon, not single chromium deposition. Trivalent chromium layer formed from PEG-containing solution was amorphous with local nano-crystalline particles, which were prominently developed on the entire surface after non-oxidative heat treatment.